Antibodies are biological molecules with remarkable affinities for their target antigens. Nature provides antibodies as part of a defense system in certain vertebrates for the elimination or destruction of foreign proteins, cells and organisms. If a certain vertebrate is presented with a foreign protein on, for example, an infected cell or an infectious bacterium, an antibody can bind its target foreign protein to direct the foreign entity to its elimination or destruction.
The selective affinity of antibodies can be used by man to target nearly any antigen desired. The antigen can be a protein on an infected cell or infectious microorganism. It can also be, for example, a protein on a cancer cell, a protein on a cell of a target tissue, a protein in the bloodstream, a protein on an inflamed or inflammatory cell or any other protein whose selective binding is useful. Antibodies have thus found use in therapy for conditions such as cancer, inflammatory diseases, autoimmune diseases and transplant rejection. The antibody can signal the immune system to destroy or eliminate a diseased cell, or an engineered antibody can carry a molecular payload to destroy the target. In certain applications therapeutic antibodies are linked to molecular shields to increase their lifetime within an organism. Antibodies have also found use as diagnostics. These antibodies can carry a label to indicate the presence of a target antigen on a cell or in a tissue. These labels are typically linked to the antibodies by covalent bonds.
To date, techniques for linking antibodies molecular entities such as molecular payloads, molecular shields and labels have been limited by their heterogeneity in degree and location of linking to the antibodies, by their low yields and by losses in activity. Typical conjugation sites include random locations on antibody chains, e.g. random amines on amino acid side chains, and the N-terminus of certain antibody chains. In such techniques, some antibodies might be linked to the conjugate at one location while some antibodies are linked to the same conjugate at another location, and some antibodies might not be linked at all. For example, the antibody is linked to one or more single-chain binding domain (scFv).
There is a need for antibodies modified at site-specific positions optimized for uniformity, yield and/or activity to further the promising use of antibodies in, for example, therapy and diagnostics.